1. Field of the Invention
The present invention relates to windings for electric devices such as transformers, reactors, super conductive devices and so forth, and, more particularly, to windings wound into a disk-like form or a helical form having an improved cooling effect.
2. Description of the Prior Art
Before turning to the description of the embodiments of the invention, an explanation will be made here as to the prior arts, in order to clarify the drawbacks of the prior art which are to be overcome by the present invention, in reference with FIGS. 1 and 2.
FIG. 1 is a schematic vertical cross-sectional view of conventional disk-coil windings for a transformer, as an example of conventional windings, while FIG. 2 is a sectional view of the windings as shown in FIG. 1 taken along a horizontal plane and showing a disk winding unit and concentric insulating sleeves disposed at the inner and outer sides of the disk winding units.
As will be seen from FIGS. 1 and 2, conventional windings of transformer have a plurality of disk winding units 4 stacked one on another. Each disk winding unit 4 consists of a conductive wire element 4a wound and disposed in an annular gap formed between an inner insulating sleeve 2 and an outer insulating sleeve 3 which are disposed around a magnetic core structure iron 1. Cooling passages 5 extending in the horizontal direction (referred to as horizontal cooling passage, hereinafter) are formed by horizontal duct pieces, between adjacent winding units 4. Similarly, cooling passages 6, 7 extending in the vertical direction (referred to as vertical cooling passages, hereinafter) are formed between the winding unit 4 and the inner insulating sleeve 2, and between the winding unit 4 and the outer insulating sleeve 3, by means of respective vertical duct pieces (not shown) extending in the vertical direction. A cooling fluid such as insulating oil is circulated through these passages by means of a pump 8 or the like, so as to cool the winding.
In the forced-cooled disk-like winding, the barrier inserts 10, 11 are disposed at a vertical spacing of several of disk windings, having alternatingly arranged fluid inlets and outlets, in the inner and the outer vertical cooling passages 6, 7. By a pair of the said barrier inserts one cooling zone is formed. Therefore, the cooling fluid flows in a zig-zag manner, from the inner vertical cooling passages 6 of the outer vertical cooling passages 7 and vice versa, so that the fluid flow may be turned at each time it passes one cooling zone. Due to the provision of these barrier inserts, the cooling fluid flow shunting from one 6 (or 7) of the vertical cooling passages to the other 7 (or 6) through the horizontal cooling passage defined between the winding units 4.
However, in the disk-like windings having the described cooling passages, it is to be pointed out that the winding units 4 within one cooling zone defined by adjacent barrier inserts 10, 11 are not cooled uniformly. Namely, the lower winding units closer to the inlet of the cooling fluid are not sufficiently cooled, as compared with the upper winding units disposed close to the outlet of the fluid, due to the presence of these barrier inserts. More specifically, the velocities of the cooling fluid through the plurality of horizontal passages formed in one cooling zone are all different, and the flow rates through lower horizontal passages are much smaller than those through the upper horizontal passages. Therefore, the uniform temperature distribution over all winding units is not obtained to an acceptable extent, even by the zig-zag flow of the cooling fluid, so as to cause a local temperature rise in each cooling zone, resulting in a deterioration of the insulation and a shortened life of the winding.
FIGS. 3 thru 6 inclusive show other examples of conventional winding for electric devices.
The winding structure as shown in FIG. 3 has been disclosed in the specification of U.S. Pat. No. 4,000,482 (Ser. No. 645,562) by Ramachaudran, entitled "TRANSFORMER WITH IMPROVED NATURAL CIRCULATION FOR COOLING DISC COILS". In this winding structure, ring-shaped partial flow barrier inserts 12 are attached to the end surface of the winding unit 4, in place of the barrier inserts 10, 11 of FIG. 2, so that each winding unit may constitute one cooling zone and that the cooling fluid may flow in a zig-zag manner through respective cooling zones.
These barrier inserts 12 do not completely close the cross-sections of the inner and the outer vertical cooling passages 6, 7, but are arranged to leave slight gaps 13 between itself and the inner and the outer insulating sleeves 2, 3. However, unfortunately, an uniform flow distribution over the all horizontal passages cannot be obtained even by the provision of these gaps 13. It is possible to decrease the pressure loss across the gap 13, by enlarging the gap 13, thereby to improve the velocity distribution over the all horizontal passages to some extent. However, to the contrary, the zig-zag component of the fluid flow is weakened correspondingly, so as to decrease the velocity of the fluid flow through the horizontal passages.
On the contrary, when the gap 13 is made too small, the pressure loss across the latter will increase to make the flow velocity distribution over all horizontal passages.
Various measures have been taken to overcome or avoid above stated difficulty in cooling the coil windings uniformly.
According to one of these measures, the electric device is used with a reduced density of the electric current through the winding element. As an alternative measure, the electric device is designed on the basis of the cooling condition of the horizontal passages 5 of the smallest flow velocity and, accordingly, the smallest flow rate, among the horizontal passages 5 of the device.
However, these measures are found impractical, because the size of the device is rendered unacceptably large.
As still another measure, an improved winding structure as shown in FIGS. 4 and 5 has been disclosed in Japanese Utility Model Publication No. 15364/71 (Appln. No. 2020/68). In this winding structure, a plurality of winding units 4 form one cooling zone, through which the cooling fluid is passed in a zig-zag manner. Insulating bodies 14a-14e, and 15 for adjusting the flow rate of cooling fluid, the height of which being successively changed are disposed in the inner vertical passage 6 between the inner ends of the winding units of alternating one of the cooling zone and the confronting inner insulating sleeve 2, and in the outer vertical passage 7 between the outer ends of the winding units of the other cooling zone and the confronting outer insulating sleeve 3, thereby to gradually decrease the area of the vertical passages, thereby to achieve the uniform flow distribution of the fluid over all horizontal passages 5 between winding units 4. However, this arrangement has a drawback that the pressure loss of the fluid is inconveniently increased and that the passage structure is rendered highly complicated, due to the provision of the large number of flow-rate-adjusting insulating bodies 14a-14e, and 15.
Japanese Patent Laid-open Publication No. 27416/76 (Appln. No. 98953/74) discloses another winding structure for improving the cooling effect. More specifically, in this winding structure, the barrier inserts 10, 11 of FIG. 2 are substituted by a specific arrangement such that the radius of the winding units are suitably increased and decreased, so that the peripheral ends of alternating winding units may be radially projected into the inner and the outer vertical passages, as shown in FIG. 6.
According to this winding structure, the pressure of the fluid through the vertical passages 6, 7 is increased at portions below the peripheral ends of the winding units projecting into these passages, while the pressure is decreased at portions of the vertical passages 6, 7 above the projecting peripheral ends of the winding units, because the flow of the fluid is restricted and released at these portions, respectively. Consequently, a pressure differential is created across the inlet and outlet sides of each horizontal passage which, in combination with the sucking force provided by the viscosity of the fluid, induces a flow of fluid through each horizontal passage 5. However, this winding structure is disadvantageous in that the electric field is concentrated to the projecting peripheral edges of the winding units in case of a short-circuiting of the windings, due to the staggered projection of these peripheral edges, possibly resulting in a breakage of the winding structure. To the contrary, the winding structure has to be made large, in order to increase the withstand voltage of the windings.